842,686 research outputs found

    What constrains Africa's exports?

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    This paper examines the effects of transit, documentation, and ports and customs delays on Africa’s exports. The authors find that transit delays have the most economically and statically significant effect on exports. A one-day reduction in inland travel times leads to a 7 percent increase in exports. Put another way, a one-day reduction in inland travel times translates to a 1.5 percentage point decrease in all importing-country tariffs. By contrast, longer delays in the other areas have a far smaller impact on trade. The analysis controls for the possibility that greater trade leads to shorter delays in three ways. First, it examines the effect of trade times on exports of new products. Second, it evaluates the effect of delays in a transit country on the exports of landlocked countries. Third, it examines whether delays affect time-sensitive goods relatively more. The authors show that large transit delays are relatively more harmful because of high within-country variation

    The effect of distributed time-delays on the synchronization of neuronal networks

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    Here we investigate the synchronization of networks of FitzHugh-Nagumo neurons coupled in scale-free, small-world and random topologies, in the presence of distributed time delays in the coupling of neurons. We explore how the synchronization transition is affected when the time delays in the interactions between pairs of interacting neurons are non-uniform. We find that the presence of distributed time-delays does not change the behavior of the synchronization transition significantly, vis-a-vis networks with constant time-delay, where the value of the constant time-delay is the mean of the distributed delays. We also notice that a normal distribution of delays gives rise to a transition at marginally lower coupling strengths, vis-a-vis uniformly distributed delays. These trends hold across classes of networks and for varying standard deviations of the delay distribution, indicating the generality of these results. So we conclude that distributed delays, which may be typically expected in real-world situations, do not have a notable effect on synchronization. This allows results obtained with constant delays to remain relevant even in the case of randomly distributed delays.Comment: 10 pages, 9 figure

    Judicial Review, Delegation, and Public Hearings Under NEPA

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    Ever since the inception of the modern computer, researchers and designers alike have been interested in the effects of system delays on users. The current study was conducted in order to examine the most central issues to the field of temporality in interaction, and presents a consolidation of a selection of publications on the subject. A distinction between two types of interactive systems, discretionary and continuous, is proposed in order to situate previous studies by the system being studied. The type of control being exerted by users differs on a fundamental level between the two types, hence affecting the effects of delays. Furthermore, an experiment was conducted to examine the effects of constant, sub-second system delays in discretionary tasks using a digitalised version of the Trail Making Test (FR-TMT, Summala et al., 2008). The experiment yielded but one significant result in form of an improvement in user response time as delays were increased. The other results showed no significant positive or negative effect of increased delays. These results are indicative that the chosen delays do not have any detrimental effects on users, in accordance with the presently coined ’theory of task interruption’. This theory considers delays as either interruptive or non-interruptive and maintains that only delays that disrupt user work-flow are to be removed from interactive systems. The current study gives reason to why some delays can be positive to user interaction, or in themselves be informative of system status, and be an integral part of a feedback structure. Further research is needed before all aspects of system delays are fully understood. New ways of looking at delays and using them in system design, like predictability and predictivity, are becoming more prevalent, and may become the focus of research and temporal design in the near future.

    PieceTimer: A Holistic Timing Analysis Framework Considering Setup/Hold Time Interdependency Using A Piecewise Model

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    In static timing analysis, clock-to-q delays of flip-flops are considered as constants. Setup times and hold times are characterized separately and also used as constants. The characterized delays, setup times and hold times, are ap- plied in timing analysis independently to verify the perfor- mance of circuits. In reality, however, clock-to-q delays of flip-flops depend on both setup and hold times. Instead of being constants, these delays change with respect to different setup/hold time combinations. Consequently, the simple ab- straction of setup/hold times and constant clock-to-q delays introduces inaccuracy in timing analysis. In this paper, we propose a holistic method to consider the relation between clock-to-q delays and setup/hold time combinations with a piecewise linear model. The result is more accurate than that of traditional timing analysis, and the incorporation of the interdependency between clock-to-q delays, setup times and hold times may also improve circuit performance.Comment: IEEE/ACM International Conference on Computer-Aided Design (ICCAD), November 201

    Can distributed delays perfectly stabilize dynamical networks?

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    Signal transmission delays tend to destabilize dynamical networks leading to oscillation, but their dispersion contributes oppositely toward stabilization. We analyze an integro-differential equation that describes the collective dynamics of a neural network with distributed signal delays. With the gamma distributed delays less dispersed than exponential distribution, the system exhibits reentrant phenomena, in which the stability is once lost but then recovered as the mean delay is increased. With delays dispersed more highly than exponential, the system never destabilizes.Comment: 4pages 5figure

    Effects of Transport Delays of Manual Control System Performance

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    Throughput or transport delays in manual control systems can cause degraded performance and lead to potentially unstable operation. With the expanding use of digital processors, throughput delays can occur in manual control systems in a variety of ways such as in digital flight control systems in real aircraft, and in equation of motion computers and computer generated images in simulators. Research has shown the degrading effect of throughput delays on subjective opinion and system performance and dynamic response. A generic manual control system model is used to provide a relatively simple analysis of and explanation for the effects of various types of delays. The consequence of throughput delays of some simple system architectures is also discussed